Haxe array & anon in Lua

anon.lua

local Anon_mt = {
    __newindex = function(self, key, value)
        if value ~= nil then
            rawset(self, key, value)
        else
            self._nils[key] = true
        end
    end,

    __tostring = function(self)
        local s = "{"
        local keys = anon_keys(self)
        local i = 0
        local len = #keys
        while i < len do
            local k = keys[i]
            s = s .. k .. ":" .. tostring(self[k])
            i = i + 1
            if i ~= len then s = s .. ", " end
        end
        s = s .. "}"
        return s
    end
}

Anon = {
    new = function()
        return setmetatable({_nils = {}}, Anon_mt)
    end
}

function anon_keys(s)
    local a = Array:new()
    for k, v in pairs(s) do
        if k == "_nils" then
            for k,v in pairs(v) do a:push(k) end
        else
            a:push(k)
        end
    end
    return a
end

function anon_del(s, f)
    s[f] = nil
    s._nils[f] = nil
end

array.lua

local Array_mt = {
    __index = {
        push = function(self, item) self[self._len] = item end,
        indexOf = function(self, item)
            for i = 0, #self do
                if self[i] == item then return i end
            end
            return -1
        end
    },

    __newindex = function(self, key, item)
        if key >= self._len then self._len = key + 1 end
        rawset(self, key, item)
    end,

    __len = function(self) return self._len end,

    __tostring = function(self)
        local s = "["
        local i = 0
        local len = self._len
        while i < len do
            s = s .. tostring(self[i])
            i = i + 1
            if i ~= len then s = s .. ", " end
        end
        return s .. "]"
    end
}

Array = {
    new = function()
        return setmetatable({_len = 0}, Array_mt)
    end
}

test.lua

dofile "array.lua"
dofile "anon.lua"

local o = Anon:new()
o["hello"] = 1
o["bye"] = nil
print(o) -- {bye:nil, hello:1}
anon_del(o, "bye")
print(o) -- {hello:1}

local a = Array:new()
a:push(10)
a:push(20)
a:push(nil)
a:push(30)
a:push(nil)
print(a, #a) -- [10, 20, nil, 30, nil]  5